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lssued March1980
28
By TNL: cN2t-0325
Chapter7. Disk StorageDrives
IBM 54M15448 Disk Storage Drives o System/3Model 15A
One ModelA2
}IBM5444DISKSToRAGE
DRIVE Two Model A2s
One ModelA2 and one ModelA3
Thef BM5444DiskStorage Driveprovides2,457,60O
through9,830,400
bytesof storage. R E M O V A B L E I S KC A R T R I D G E S O R5 4 4 4
D F
The5444isavailable sixmodels:
in
Tracks/ No. of Total Capacity Avg Access
I (in bytes)
Model Surface Disks2 Time
1 104 2 2,457,600 1 5 3m s
A1 't04 2 2,457,600 86 ms
2 204 2 4.915,200 269 ms
A2 204 2 4,915,200 1 2 6m s
3 204 'l 2,4s7,600 269 ms
A3 204 2,457,600 1 2 6m s
I
I B M r e s i d e n tc o n t r o l p r o g r a m r e q u i r e so n e t r a c k p e r s u r f a c e
f o r c u s t o m e r e n g i n e e r s . I B M d i s k s y s t e m sp r o g r a m m i n g
s u p p o r t r e q u i r e s3 t r a c k s p e r s u r f a c ef o r a l t e r n a t ed a t a
t r a c k s . S y s t e m su s i n g t h e s e p r o g r a m sa r e t h e r e f o r e l i m i t e d
t o 10 0 o r 2 0 0 t r a c k s p e r s u r f a c e ,a c c o r d i n gt o t h e m o d e l
selected.
2
E a c h m o d e l h a s o n e r e m o v a b l ed i s k ( F i g u r e 7 - 1) . M o d e l s
'l,
A 1 , 2 , a n d A 2 a l s o h a v e 1 p e r m a n e n td i s k . B o t h s u r f a c e s
of eachdisk are used.
7-1. IBM5440DiskCartridge
Figure
All six models the 5444 Disk Storage
of Driveperform Each5444 uses removable
a IBM 5440 Disk Cartridge
at a data rate of 199 kilobytesper second(tb%) at a (Figure7-1). Usingremovable cartridgesprovidesvirtually
rotationspeed 1500 rpm.
of unlimitedoffline disk storage allowsdata interchange
and
betweenalt 5444 modelson all I BM System/3models.
The 5/,44can be orderedwith the followingconfigurations However, data recorded the second
on 100 cylinders a
of
of models: 5'140by an IBM 5444 Model 2, A2,3, or A3 cannot be
readby a5444 Model 1 or A1. Also, a544Odisk initialized
o System/3Model 8 on a 5444 Model 1 or Al is.notinitialized the second
on
O n eM o d e l A l I00 cylinders.
One ModelA2
Two ModelA2s Careand handlingprocedures the 5440 aredescribed
for
One ModelA2 and one ModelA3 in IBM 5440 Disk Cartridge Handling Procedure Manual,
G426-1598.
o System/3Model 10
IBM 5448 DISK STORAGEDRIVE
Standard Speed Access High Speed Access
The IBM 5448 Disk Storage Driveprovides additional
an
One Model 1 One ModelAl 9,830,400bytesof storage the System/3Model 8 and
for
One Model2 OneModelA2 M o d e l1 0 . l t i s a v a i l a b lie o n e m o d e l( A 1 1 .
n
Two Model 2s Two Model A2s
One Model2 and One ModelA2 and
one Model3 one ModelA3
Disk StorageDrives:.544415448 7-1
The 5448 is housed its own enclosure contains
in and two 544415448D rSK O RGAN I ZATTON
disk drivesidentically designed.Eachdrivehastwo fixed
disksattached a commonspindle
to and is capable of Eachsurface eachdisk contains
of 204 tracks. The tracks
storing4.915,2OO byteswith an average access time of that arerelated eachother in the verticalplaneon a
to
126 ms. Eachdisk has408 tracks(204 on eachsurface). singledisk areconsidered form a cylinderasshownin
to
The IBM resident control program requires one track per Figure7-2. On driveswith two disks,the corresponding
surface for
reserved customer engineers. IBM disk systems cylinders both diskshavethe same
on cylindernumber.
programming supportrequires three tracksper surface for
204 concentriccylinders (one for
alternate datatracks. Systems using theseprograms are,
therefore, limitedto 200 tracksper surface.
SYSTEM ONFIGURATION
C
Model 8
The minimumSystem/3Model8 configuration
that the
5448 is designed operate
to with is:
o 5408P r o c e s s i n gn i t , M o d e lA 1 4 ( 1 6 K b y t e s l
U
. 5444 D i s kS t o r a g D r i v e M o d e l A 2( R 1 ,F 1 )
e ,
N 7i
. 5203 Printer,
one of the following:
Model 1 Cylinder 0
Model2
Model3
Note: The same cylinder address is used, for all corre-
o Input/outputdevice, one of the following: s p o n d i n gt r a c k s o n t h e d i s k s , F o r e x a m p l e ,t r a c k 1 5 o n
5471 Printer-Keyboard, Model 1 both the upper and lower surfacesof disks 1 and 2 are all
Directlyattached 3741 DataStation,Model 1 or 2 considered to be bands of data on one cylinder, so all four
Directlyattached 3741 Programmable Work Station, bands have the same cylinder address. On the54441544,
the same track on both the upper and lower surfacesof a
M o d e l3 o r 4
s i n g l ed i s k a r e c o n s i d e r e dt o b e a c y l i n d e r ,
Note: The 5448 cannot be attachedto a Model 8 with the
S e r i a l n p u t / O u t p u C h a n n e(lS I O C ) .
t FigureT-2, 54214Cylinder Concept
Model10 Disk System
The minimum System/3 Model 10 Disk System configura-
tion that the 5448 is designed operate
to with is:
o 5 4 1 0 P r o c e s s i n gn i t , M o d e lA 1 3 ( 1 2 K b y t e s )
U
. 5 4 4 4 D i s kS t o r a g e r i v e ,M o d e l2 o r A 2 ( R 1 , F 1 )
D
P r i n t e ro n eo f t h e f o l l o w i n g :
,
5 2 0 3P r i n t e rM o d e l1 , 2 , o r 3
,
1 4 0 3P r i n t e r M o d e l2 o r N 1
,
Input/outputdevice, one of the following:
5424 MFCU, ModelA1 or A2
1 4 4 2 C a r dR e a dP u n c h M o d e l6 o r 7
,
Note: The 5448 cannotbe attached a Model 10 Disk
to
System with the 5445 DiskStorage.
54,4r'.lil4B Track Format
Eachtrack is divided into 24 sectors{Figure7-3). Each
sectorhasan individual address. sectorcontains:
A
. lndex Marker - A mark that is fixed for eachdisk and
provides orientationinformationto the controlling
circuits. lt is the startingpoint for everytrack.
. AM - Address markeris a specially written groupof
bits usedto indicatethe start of a new sector.
. lD - The sectoridentifier. This groupof 6 bytes
contains bytesfor uniqueidentification that sector
3 of
for that disk, and 3 bytes of checkcharacters.
Data - The data areaof the sectorcontains256 bytes
of data and 3 bytes of check characters.
Gaps- Gaps specially
are written areas the disk
on
usedto separate definethe other elements the
and of
sector.
Tracko_
I
I
) ) '
Each Track
' Sectors5-21
l-/
.'\Nqs'-t --Y
z \
Sector 22 Sector23 Sector 0 Sector 1 - Sectors
2-22
El Gap P e r m a n e n tl n d e x M a r k e r ( b e t w e e n
sectors 23 and 0 on all tracks)
Figure7-3. Ssctor Layout
Disk Storage Drives:. 544415448 7-3
54441U48 Sector ldentifier Format and Addressing Cylinders numbered through203, countingfrom the
are 0
outer cylinder. IBM customer engineers cylinder203
use
The identifierareaof a sector(lD) contains flag byte, 2
a for diagnostic functions, this cylindershouldnot be
so
bytesof address information,and 3 bytesof checkinfor- usedfor permanent storage.Tracksin cylinders1,2, and
mationasshownbelow: 3 are usedby IBM program products alternate
as tracksif
tracksin cylinders through202 become
1 defective;there-
Flag Address Check Characters fore, if f BM program products used,
are cylinders1,2, and
3 are reserved. Tracksin cylinders and 4 through202
0
F c S cc cc BCA can be usedasstandard datatracks.
F Flagbyte. This byte contains flagging information Sectors within a track are identifiedby their physical
in bits 6 and 7. All other bits in this byte should positionon the track with relationto the indexmarker
be 0. and by the surface the disk on which they reside.The
of
sectors the uppersurface the disk are numbered
on of 0
C Cylinderbyte. This byte contains binary
the through23 starting from the indexmarker,and the
numberthat corresponds the physical
to location sectors the lowersurface numbered through55.
32
on are
of the track on the disk. A specificsectoraddress, then, consists a drivenumber
of
(upperor lowerdisk),a cylindernumber,and the sector
S Sector byte. The 6 leftmost bits in this byte number. However, only the cylindernumberand sector
represent binarynumberof the sector. Sectors
the numberarerecorded the disk.
on
on the uppersurface the disk havesector
of
numbers from 0 through23. Sectors the lower
on
surface the disk havesectornumbers
of from 32 5444 (ONLY} DISK OPERATINGRESTRICTIONS
through55.
The disk drivedrawers cannotbe opened unless system
CC Cycliccheck. The attachmentgenerates
these2 power is on and the disk start/stopswitch on the system
bytesand usesthem for checkingpurposes. control panelis in the stop position. The OPENlight on
the systemcontrol panellightswhen it is safeto open
BCA Bit count appendage.
Anotherchecking
byte the the drawers. We recommend that the drawersbe kept
attachmentgenerates, closed unless disk cartridge beinginserted removed.
a is or
A cartridgeshouldalwaysbe storedon the drive to prevent
The address any individual
of sectoris contained the
in dust from entering drive.
the
second and third bytesof the identifier. Sectors occupying
the same.physical locationon the lowerdisk and on the upper The 5440 disk cartridgemust be stored in the operating
(removabf on the 5444) diskshaveidenticalbinary
e environment at least2 hoursbeforethe cartridge
for is
numbers in the cylinder and sector byfes. Useof a sector usedfor processing.
requiresthat the drive (1 or 2) and the disk (loweror
upper Iremovable the 5444] ) containing desired
on the
sectormust be specified.
544/.15/,48DISK OPERATIONS SeekOperation
5444 15,4,48
For eachdisk operation, address the disk control
the of The access mechanism the selected
of drive is moveda
field must be storedin the disk control address
registerand specifiednumberof cylinders and the upperor lowerhead
the address the first byte of the disk datafield must be
of for the specified
disk is set for future read,write. verify,or
storedin the disk read/write addressregister. scanoperations. The numberof cylinders cross
to and the
headto set are specifiedby the disk control field as de-
The disk control field is 4 byteslong;thesebytesare scribedbefore.
designatedF-byte, C-byte,S-byte,and N-byte. The bytes
are usedasfollows: The N-bytespecifies numberof cylinders access
the the
mechanism travels
duringthe seek.
Byte Use
Bit 7 of the S-bytespecifies directionof movement.
the
This is the first byte in the field and the byte Forward(bit 7 = 1) is from cylinderO to 2O2. The headis
addressed the disk control address
by register. In specified bit 0 of the S-byte.
by
seekoperations, byte is not used. In other
this
disk operations, contains lagbits in bits 6 and 7.
it f The recalibration function is executed specifying seek
by a
in the reversedirectionand the numberof cylinders move
to
c This second byte of the field contains binary
a (greater than or equalto 224!-. The recalibratefunction
numberthat designatescylindernumber. This
a causes access
the mechanism returnto cylinder0 and
to
byte is not usedon a seekoperation. selects read/writehead0, regardless the condition of bit
of
0 of the S-byte.
The functionof this byte (the third byte in the
field) depends the operation:
on Note: On high performance disk drives,recalibrationshould
be usedonly for error recovery,because recalibrationforces
SeekOperation.' Bit 0 selects headto be
the a low speedseekin a reversedirection.
=
lused (0 head0 for uppersurface; = head1
1
lfor lowersurface).Bits 1 through6 arenot The C-byte,0 bit in the sensebyte is set when the mechan-
directionof seek(0 =
used. Bit 7 selects ism reaches
cylinder0, and can be interrogated the
by
toward decreasing cylindernumbers; =
1 programwith a sensel/O instructionafter the seekis
toward increasing cylindernumbers). complete.
All Other Operations: Bits 0 through 5 hold Seekoperationis begunby issuing SIO instruction.A
an
the binaryrepresentation the sectorlD
of second SIO instruction can be issued the same
to disk drive
number. Bits 6 and 7 are not used; 7 must
bit if a read,write, or scanoperation specified.The second
is
be 0. instruction accepted
is provisionally executed no
and if
errorsoccurin the operation the seekinstruction.A sub-
of
This lastbyte in the field specifies
eitherthe num- sequent SIO instruction eitherdisk causes CPUto
to the
ber of cylinders movethe access
to mechanism loop on that instruction until the read,write, or scanopera-
for a seekoperationor the numberof sectors to tion ends. However,seekcommands both drivescan be
to
usefor any other operption. For operations other executed concurrently thereis no intervening
if SIO read,
than seek, this binarynumbermust be 1 less than write, or scaninstruction.
the actualnumberof sectorsdesired. For example,
if 1 sectoris to be used.the N-bytemust contain No data in storageis changed this operation. Test l/O
by
a 0; if 10 sectors to be used(a multiple-sector
are for busy or advance programlevelon busy doesnot detect
operationl, the N-bytemust containa 9. busy unless read,write, or scaninstruction hasbeenpro-
a
visionallyaccepted. The sense for seekbusy is on, how-
bit
ever,for interrogation the sense instruction.
by l/O
A seekto the cylinderat which the access
mechanism
is
locatedis completedimmediatelybecause access
no mech-
anismmotion is required.However, headis selected
the
according bit 0 of the S-byte.
to
Disk Storage Drives: 544415448 7-5
54446448 AccessTime AccessTime for 5444 Models Al, 42, A3, and 5448:
For the high performance disk storagedrivemodels, access
Accesstime is the intervalfrom the receiptof a seekcom' times are not necessarily samefor both forward and
the
mand until read/writeheadmovementstops. reverseseekoperations, The more important access times
(for both forward and reversedirections)for thesedisk
drivesare:
AccessTime for the 5tM4 Models |, 2, and 3 Only: Figure
7-4 showsthe approximatetime reguiredto seekacross any o The access movement 28 milli'
time for a 1-cylinder is
number of cylindersfrom 1 to 200' Access time can also seconds all threemodels.
for
be determined from the followingformula:
o The normal average accesstime lor a5444 Model A1
Seektime for 1 cylinder= 39 milliseconds is 86 milliseconds; 5444 ModelsA2, A3, and 5448,
for
=
Seektime lor 2 or more cylinders 47 + 3.42 (N'2) the normalaverage time is 126 milliseconds'
access
milliseconds This is the average time across cylinder
access 67
addresses with the exceptionof when a forward seek
whereN = the numberof cylinders be crossed'
to terminates cylinderaddress through203.
in 170
o The maximumaccess time (the time takenfor the
750 access mechanism cross
to the maximumnumberof
720 cylindersavailable eachmodel)is 163 milliseconds
on
@o for 99 cylinders ModelAl ; for 5444 Models
on 42,
660 A3, and 5448,the accesstime is 255 milliseconds for
(xx) 199 cylinders.
6m
570 To Determine Approximate Maximum AccessForward
540 Time: Access times for accessforward operationsare not
510 dependent solelyon the numberof cylinders traveled,but
0
alsodependon wherd:ihe accessforward operationstermi-
.150
nate. For this reason, simplegraphcan be drawnshow-
no
4m
times for alltpossible
ing access forward operations.
access
390
tF
360
Figure7-5 showsma:.dtnum accesstime curvesfor access
3:X'
a,o forwardoperationsstarting from several differentcylinder
270 addresses. Eachcurve is labeledwith its appropriatestart-
2& ing cylinderaddress.Intermediate values may be deter-
210 minedby interpolation.
180
150 To determine access
the time for any forwardoperation fol'
120 low the curvecorresponding to the startingcylinderaddress
90 with the cylinderaddress that is
until the curvecoincides
60 (horizontal The corresponding access
beingaccessed axis).
30
time is then readfrom the vertical axis in milliseconds. For
0
example,to determinethe access time for an access opera-
10 20 30 4{r 60 60 70 80 90 100 10 20 30 trc 50 60 70 80 9() 2q)
tion from cylinderaddress to cylinderaddress
040 120' fol-
-l-r-l- Maximum time one direction
access low the curvecorrespwrding cylinderaddress
to 040 until
maximumaccess
Average time the curveis aligned wilh cylinderaddress on the hori-
120
- Maximumaccesstime oppositedirection
zontalaxis. The required access time indicated the ver-
on
tical axis is 140 milliseconds.
Timing (5tt44Models1,2, and 3 onlyl
Figure74. Access
32
c
o
t
5
.E1
o
E
F
o
o
tr
00 20 40 .t20 .t40
60 80 100
D e s ir e d C y l i n d e r A d d r e s s
Figure 7'5. Maximum Access Time tot g444 Models A1, Az, A3, and 5448 (Forward Directionl
c
o
o
.2
5
.g
o
E
tr
o
a
o 20 40 60 80 100 120 140 160 180
N u m b e r o f C y l i n d e r sT r a v e l e d
Figure 7-6. Maximum Access Time tor 5444 Models A1, A2, A3, and B[4.8 (Forward or Reverse Directionl
Disk StorageDrives: 544415448 7-7
To CalculateMaximum 5/U4/5448 Access Forward Time: For example, determine maximumaccess
to the time for
Approximatemaximumaccess timesfor access forward an access
operationfrom cylinderaddress 50 to cylinder
1
operations shownin Figure7-6. However,
are someaccess address200:
forwardoperations finishingabovecylinderaddress 170
haveaccess timesgreaterthan that indicated Figure7'6.
in 1. From Figure7-7, locatethe point of intersection
of
(Reverseoperations not affected.)
are the presentcylinderaddress (cylinder 1
address 50)
and the new cylinderaddress (cylinderaddress200).
Figure7-7 showsall possible accessoperations. The chart is The point of intersection in the shaded
is area.
dividedby a diagonalline into two regions
covering access
forwardoperationsand access reverse
operations. The 2. From Figure7-6,determine that maximumaccess
accessforwardregionis further subdivided into three difference 107
address
time for a 50-cylinder is
areas, milliseconds.
To determine the maximumaccess time for any accessfor- 3. From Figure7-8,determine that the additional
time
ward operation, find the point wherethe from cylinder to be addedis 39 milliseconds.
address (horizontalaxis)and the to cylinderaddress (verti-
cal axis)intersect.The areain which this point of intersec- Therefore, total maximumaccess
the time for this access
tion occursdefines how the access time is calculated,as o p e r a t i o ns 1 4 6 m i l l i s e c o n d s 0 7+ 3 9 = 1 4 6 m i l l i s e c o n d s ) '
i (1
follows:
1. Unshaded directly
time determined
area-access To Calculate AccessReverceTime: Figure 7-6 showsthe
from Figure7-6. maximumaccess that the
time for the numberof cylinders
mechanism
access crosses duringan access
reverseoperation.
2. Shaded area-accesstime determined Figure7'6
by
plusan additional
time as indicated the chart
by Note: Readymay be dropped if an access reverse
operation
(Figure -8).
7 moretracksthan the actualnumberof tracksfrom
specifies
the present
track to the home position. lf readyis dropped
3. Cross-hatched time shownin Figure7-9.
area-access and no permanent hardware stop the disk drive
fault exists,
andthen restart disk driveto establish file ready
the a
condition.
7-A
o
o
c
>
F
Access
Reverse
Operations
From Cylinder Address
Figure 7-7. Access Time Chart for 5444 Models A1 , AZ, A3, and 52148
Disk Storage Drives: 544415448 7-9
From Cylinder Address
(o
I E (o
r s c{
o) 8 gI N @
N
s
c!
6
N
N o $
sl s
o
st I (\l
u) s tt
E c{
@
o)
203 3 3 6 I t 2 1 t 1 5 1 2 1 24 2 l 30 33 339 42 45 18 t8 t 1 51 5 t 54 57 60
202 o 3 3 6 9 1 2 1 5 1 5 1 8 2 1 24 21 2 7 30 39 2C 42 t5 i l 5 1 t 1 54 57
201 o 3 3 6 I 2 1 5 1 5 1 8 2 1 24 2 7 2 7 ? l 36 lc 39 42 f5 1 51 54
200 o 3 3 6 9 1 2 1 5 1 5 1 8 2 1 24 2 7 21 2 ( 33 36 39 39 t2 4 5 r8 51 i 1 54
r99 0 3 3 6 a 2 1 5 1 5 1 8 2 1 24 21 2 7 3C l6 39 39 ,9 4E 45 51 5 1
198 0 3 3 6 9 l 2 1 t 5 1 8 2'l z4 2 7 21 30 3336 l6 ]9 39 4 2 15 48
t97 0 ? 3 6 9 1 2 1 5 1 5 1 8 21 24 27 2 7 l3 33 33 39 39 42 45 48
196 0 3 3 b 9 1 2 1 5 1 5 1 2 1 24 2 7 27 30 l0 5 J 3: 36 JV 39 45 4 5
1 i 33 36 t9 l9 4 2 4 2
195 o 3 3 6 o 1 2 1 5 1 t 1 8 21 24 21 27 27 l0
194 0 3 3 o 9 1 2 1 5 1 5 1 8 1 24 24 27 t 7 21 30 33 l3 39 39 t2
't
193 0 3 J 6 9 1215 1518 24 24 27 2 7 3C 33 36 39 39
192 0 3 3 6 I 1 2 1 5 1 5 1 8 21 z1 1 24 2 7 2 7 30 33 36
o
191 0 3 J b I 12 15 8 18 1 24 21 2 1 33 36
190 0 3 3 6 I 1215 1515 18 2 1 24 2 7 27 30 33
o
189 0 J 3 6 I 1 2 1 2 1 5 1 5 1 8 1 21 24 27 2 7 30
= 188 0 J 3 6 I I l 2 t 5 1 5 8 21 1 24 2 7 ) 1 30
O
187 0 3 3 6 9 9 1 2 l 5 1 5 1 8 I 21 24 27 2 7
F o
186 0 ? 3 o 9 2 5 1 5 t 8 21 21 24 24
185 0 3 ? 6 o 9 1215 1518 I 1 24
184
183 0 3 3 t) I 9 1 2 t 5 1 5 8 1 8
182 0 3 3 6 I I 2 15 J 18
181
180 0 2 3 6 9 9 2 12
179
1n
1?7
176
175
174
N o t e : T o r e d u c e t h e s i z e o f t h e c h a r t , t h e f r o m c y l i n d e r a d d r e s s a x i s i s n o t c o n t i n u o u s .l f t h e r e q u i r e d c y l i n d e r a d d r e s s i s n o t l i s t e d , u s e
t h e n e x t h i g h e r c y l i n d e r a d d r e s s . I n s o m e c a s e st h i s w i l l m e a n t h a t t h e a d d i t i o n a l a c c e s s i m e o b t a i n e d f r o m t h e c h a r t i s a m a x i m u m o f 3
, t
m s g r e a t e rt h a n t h e t r u e a d d i t i o n a l a c c e s s i m e .
t
T h e c h a r t s p e c i f i e st h e n u m b e r o f m i l l i s e c o n d st h a t m u s t b e a d d e d t o t h e a c c e s s i m e g i v e n b y t h e g e n e r a lc u r v e i n F i g u r e 7 - 7 , f o r t h e
t
r a n g eo { c y l i n d e r a d d r e s s e sn d i c a t e d .
i
Figure 7-8. Additional AcceJ Time Chart (54rt4 Models A1, A2, A3, and 5zl48l
7-10
20 25 30
N u m b e r o f C y l i n d e r sT r a v e l e d
For a on*cylinder access: For an access more than one cylinder address
of above cylinder | 70:
Maximum accessime = 28 milliseconds
t Maximum =
time in milliseconds 32 + 3.42 (N-2)
access
2 < N< 3 3
N = Number of tracks to be crossed
Figure7-9. MaximumAccgss
Timesfor Accesses Cylinder170 (ForwardDirectionl
above544415448
544415448 Read Data Operation a seekoperation.)The datais transferred processing
to
unit storage,starting the processing storage
at unit address
This instruction transfersdata from the selecteddisk to specified the disk dataaddress
by register.Succeeding
main storage.Datais transferred multiples 256 bytes
in of bytesarestoredin progressively higherlocations,because
(the contents an individual
of disk sector). the5444/5448automatically updates disk dataaddress
the
register that it pointsto the storage
so address
wherethe
lf reading startedat sector0, all4Ssectors
is from corres- next byte of data is to be stored.
pondingupperand lowertrackson the same disk can be
readasthe resultof a singlereadoperation.Only consecu- Whenthe N-byteof the disk control field specifies that
tive sectors readwhen multiplesectorreading
are is more than 1 sectoris to be read,the 5444/5448 auto-
indicated. maticallyupdates S-byteof the disk control field each
the
time a sectoris readso that it contains address the
the of
Reading beginswith the sectorspecified the S-byteof
by next highersectoron that cylinderand disk. After the
the disk control field in mainstorage.(Bit 0 of the S-byte 544415448 readsector23 and stored its data, the
has
for this instructiondoesnot selectthe head,but is usedfor 5444/5448automaticallyswitchesheadsto readsector32
checking only; headselection be accomplished
can only by from the associated track on the lowersurface the disk
of
(the other track on the same cylinderon that disk). The
Disk StorageDrives: 544415448 7-11
readoperationthen continues.(Sectoraddresses cannot 5444 15448Readldentifier Operation
overflowfrom disk to disk because
eachdisk contains
identical
addresses commoncylinders;
for that is, for This operation transfers sectoridentifier(F-, C-,and S-
the
cylinderswith the sametrack number.) byles)from the selected disk to storage.The operation
startswith the first identifierto comeunderthe headafter
Duringreadoperations, 5444/5448compares disk
the the the instructionis executed.lt transfers fitst sector
the
control f ield with the sectoridentifierfieldson the disk identifierit findsto the address designated the disk
by
track to find the first sectorto be read. The comparison is control address register.lf an error is found in this identifier,
repeated eachadditional
for sectorto be read. lf the disk the next sectoridentifieris readand transferred storage
to
control field and the sectoridentifier f ield fail to match, starting the originaladdress
at contained the disk control
in
the operationterminates after the data portion of that address register.The operationis terminated the transfer
by
sectoris transferred main storage
to evenif other sectors of the first sectoridentifierfound without an error,or by
remainto be read. no recordfound. or by equipment check.
Two other abnormalconditionscause terminationof the The disk control unit is busyto any new operationexcept
reading operation. Reading terminated the end of any
is at sense while the readidentifieroperationis being
l/O
sectorin which an error is detected if the sectorreadis
or performed.
the lastsector(sector55) in the cylinder.
The informationcontained the disk control field at the
in
Duringa readoperation, attachment
the generates cyclic
2 beginning this operation not usedbut is destroyed
of is by
check(CC)bytesand a 1-bytebit count aFipendage from the informationreadin from the disk. At the termination
the data that has been read,and compares theseto the of this operation, first 3 bytes(F-, C-,and S-)of the
the
CC bytesand bit count appendage readbackwith the data, disk control field containthe lastsectoridentifier read
providinga data check for readerrors. During multiple from the disk. The last (N) byte of the disk control field
sectorreads, operationis terminated the end of any
the at is not changed. This operation doesnot switchreading
sectorin which an error is detected exceptthat an equip- between upperand lowersurfaces the disk.
the of
ment check causes immediatetermination. The data
portion of the error sectoris storedin storageand the At the end of the operation, disk control address
the register
544415448 disk dataaddress register updated.
is contains originaladdress
the unlessthereis an equipment
check. With an equipment check,the contents the
of
The readoperationendswhenthe N-byteof the disk con- registermay or may not containthe originaladdress.
trol field reaches FF and the datafrom that sectorhas
hex
beentransferred. The numberin the N-byteis decremented
by 1 at the beginning eachsectortransferred,
of 544415448ReadData DiagnosticOperation
At the end of the operation. 4 bytesof the disk control
the This operationis similarto a readdataoperation. Reading
field contain informationaboutthe progress the opera-
of always begins the index marker. Up to 48 sectors
at can
tion. The numberof sectors processed equalto the
is be read (the entirecontents the cylinder),but no more
of
originalvalueof the N-byteminusthe valueof N at the than 24 sectors should be read. Exceeding 24-sector
the
end of the operation, unless sectors
all requested were limit increases chances
the of reading wrongdata field
the
processed. all sectors
lf havebeen processed, valueof
the into storage.The data portion of the recordis readand
N at the end of the operationis hex FF. The S-byteof the placed storage
in beginning the address
at in
specified the
disk control field at the end of the operation contains the disk dataaddress register.One is subtracted from the N-
identifierof the lastsector processed unless there is a byte and addedto the S-byteof the disk control field for
missing address markeron the disk or no sectorcould be eachsectorread. The data address the disk dataaddress
in
found with an identifierthat matched that in the disk register returned
is to its originalvalueat the beginning of
control field. lf no sectorwas processed, S-byte in the
the eachsectorso that successive datafieldsoverlayeachother
disk control field is the S-byteof the first sectordesired. in storage.The operation endsat the end of the sectorin
lf an address markeris missing and a sectorwasprocessed which the N-byteis reduced hex FF, the end of the
to
in a multisector operation, S-bytein the disk control
the cylinderis detected