These instructions cover t~e following disk -storage op-erations:
Read Write
Provide an access arm and seek, or branch if arm not available.
Release access arm for further use.
All of these codes are in the 90's; position 0 is always 9. The read and write codes are ±91 and ±92. Seek is +95, and an access arm is released for further use by the program by a -95 instruction. In the case of read,
I~~~---~d)---~
~~---4~I~~---~
... --- ...
7301 Core Storage
Unit
Accumulator 3
~ ______ ~~~---~b)---t~~~~~
7601 Arithmetic and Program Unit
@ Completion of Seek
<W
Programming Address Check@ Machine Address Check
@ Validity Check
o
Compare Check on Write7300 Disk Storage Unit
FIGURE 159. DISK STORAGE AUTOMATIC CHECKING FEATURES
write and seek, the stored program initiates the opera-tion and can continue while the disk unit is operating.
When a read or write operation is completed, the main program can be signalled for priority. A seek operation automatically initiates a priority signal at completion.
Disk Storage Control
±91, ±92
MACHINE DESCRIPTION: The disk-storage read/write operation codes are similar to the tape control codes. All read and write operations are incor-porated in ±91 and ±92. With each code, the sign determines whether the read or write operation will initiate a normal-condition priority signal when the operation is completed; plus means that it will, minus means that it will not. (Unusual-condition priority occurs regardless of sign. See section on A utomatic Priority Processing.)
The only difference between 91 and 92 in read-ing and writread-ing is the channel involved; 91 speci-fies that channel control 1 is to be used for the flow of data in a read or write operation, and 92 is used for channel control 2. Position 5 of the instruction determines whether the operation is read or write. can read or write data through either chan-nel. The channel is determined here.
The address of the first record-definition word to be read into or written from (in-dexable) .
EXAMPLES: To read a disk-storage record through channel 2 into the core-storage area for which word 1204 is the first RDW, and signal for normal-condition priority at completion:
SOl 23 4 5 6789 +92 00 x 0 1204 Position 4 can contain any digit.
To write a disk-storage record via channel 1 from the core-storage area for which the first RDW is: word 2700 indexed by positions 2-5 of IW 84;
with no normal-priority signal at completion:
SOl 23 4 5 6789 -91 84 x 1 2700 Position 4 can contain any digit.
DATA FLOW: The flow of data in disk read and write operations is described in the section on Block Transmission. Data flow is the same as for tape read and write operations.
REGISTERS AFFECTED: The record-definition register, transmission registers A and B, the unit adder, and the RDW address register. (None of these registers is addressable.)
TIMING: The disk read-write commands themselves take about 60 microseconds, just as the tape for the read operation itself (one complete revolution) average read time (88 mini-mum, 138 maximum)
A disk-write operation doesn't have to wait for the beginning of the record on the track. The op-eration begins as soon as the setup for the access register is completed. The automatic compare check for every write operation requires an extra disk revolution, during which the information writ-ten on the track is read back and compared with
for the write operation itself (one revolution) taken for the machine-address check: The address in the 2-word gap is compared with the address in accumulator 3. In these cases, the write operation must wait for the two-word gap to pass under the read/write head. This adds 25 milliseconds aver-age rotational delay to operation time, making a
MACHINE DESCRIPTION: The seek operation code, +95, performs four functions:
1. Provides the file-unit number and places it into position 4 of accumulator 3. The module Automatic Priority Processing.) For this reason, the Autocoder mnemonic for +95 is PDS.
INSTRUCTION FORMAT: SOl 23 45 6789 SOl +95
23 Indexing word. The address in positions 6-9 is modified by positions 2-5 of the indexing word specified here.
45 Not used.
Label OPERAND Basic Autocoder---l Autocoder
30 35 40 45 50 55 601 65 70
FIGURE 160.
Milliseconds
900 ___ _
-~- --- ----
-~~-- -~~-- -~~-- -~~-- -~~-- ------.----.-..
---~~---.-
1 1 1 1
-Track 99 To Track 99
,,---.---~
-==r--
~. _ -500 f - - - r -
--=--- ---
--~- c-c--"
1 1
-
-~--~--
-- --
-- -- I -- -- --
-400 --~-- --.. ~
1 10 20 30 40 49
Number of Disks
FIGURE 161. SEEK TIME - DIFFERENT DISKS
Assume access arm 2 is available. Address in accumulator 3 after the instruction:
S012 3 4 5 67 89 Sxxx 2 3 6 28 47
(In any configuration of Model 1 and 2 units, module 6 designates file unit 3.) The program in-struction to initiate the seek is:
SOl 23 45 6789 +95 00 xx 4600
Positions 4-5 can contain any digits.
DATA FLOW: There is no movement of data in a seek operation.
If a seek is initiated, the address in accumu-lator 3 is moved to the access register for the arm that was provided, and the arm is sent to the track address.
If a seek cannot be initiated, the' contents of po-sitions 6-9, after indexing if so specified, are sent to the instruction counter.
REGISTERS AFFECTED: Accumulator 3 and the access register for the provided access arm. In the cases of any arm being provided (3-9 in position 4 of accumulator 3), the number of the arm that is made available replaces the digit in that position.
MILLISECONDS 250
----
!-""200
~.--... 1""'"
,.,
. /
~
. / 150 /
,J
/ / 100
50
10 20 30 40 50 60 70 80 90 99 NUMBER OF TRACKS
FIGURE 162. SEEK TIME - SAME DISK
TIMING: The duration of a seek operation depends on how far the access arm has to go. To seek a track on another disk, the access arm moves horizon-tally, vertically, and horizontally again. The mini-mum time, from the outside track (00) of a disk to the outside track of an adjacent disk, is about 445 milliseconds. The maximum length of a seek operation is from track 99 of the top disk (face 00 or 50) to track 99 of the bottom disk (face 49 or 99), or vice-versa. This takes about 855 milliseconds. Figure 161 shows the maximum timings for seek operations using different disks.
For a seek to a different track on the same disk (disk face either the same or different by 50), the arm must move horizontally only. The timing ranges from 100 milliseconds for a movement of one track, to about 235 for 99 tracks (Figure 162).
The +95 operation itself takes 48 microseconds if an access arm is provided and a seek initiated.
(This is the time taken before the next instruction can be executed.) If the program branches because of an arm being unavailable, the operation takes 24 microseconds.
AUTOCODER EXAMPLE (Figure 163): SUB1 is word 1561. The assembled instruction is:
SOl 23 45 6789 +95 00 00 1561
Label OPERAND Basic Autocoder----.-l Autocoder
25 30 35 40 45 50 55 601 65 70
FIGURE 163.
Disk Arm Release
-95 DAR
MACHINE DESCRIPTION: Once an access arm availability latch has been turned on by a +95 PDS instruction, it can be turned off only by a -95 DAR instruction.
This means that it is unavailable for another seek operation until released.
INSTRUCTION FORMAT: Sal 23 4567 8 9 Sal -95
23 Indexing word. Although positions 6-9 do not represent an address, they can be mod-ified by the value in positions 2-5 of the IW specified here.
4567 8 9
Not used.
0, 1, or 2; determines the access arm to be released
0, 1, 2, or 3; determines the file unit con-taining the arm.
EXAMPLE: To release access arm 2 in file unit 3:
Sal 23 4567 8 9 -95 00 xxxx 2 3
Positions 4-7 can contain any digits.
REGISTERS AFFECTED: The access register for the des-ignated access arm.
TIMING: 36 microseconds.
COMMENTS: The programmer never needs to know which arm was used in a seek operation, in order to release it with the DAR instruction. At the com-pletion of each seek, read, or write operation, the access arm and file-unit number are automatically placed in positions 4 and 5, respectively, of index word 99. (They are actually part of the address of the final status word, as described in the sec-tion on Automatic Priority Processing.) Normally, the DAR instruction is given immediately after the last read or write operation for that arm, releasing it for a subsequent seek instruction. If the DAR
instruction has 00 in positions 8-9, and is indexed by IW 99, the desired access-arm and file-unit number will be obtained. The DAR instruction looks like this:
Sal 23 4567 8 9 -95 99 xxxx 0 0
In Autocoder, this would be as shown in Figure 164.
AUTOCODER EXAMPLE (Figure 165): The assembled instruction is:
Sal 23 4567 8 9 -95 00 0000
a
3Label OPERAND Basi c Autocoder----l Autocoder
30 35 40 45 50 55 601 65 70
FIGURE 164.
25 30
Label OPERAND
35 40 45
Basi c Autocoder----l
50 55 601
Autocoder
65 70
FIGURE 165.