IBM 7090 User Manual

3. O. 00 CPU INTERNAL FUNCTIONS
3.1.00 FUNCTIONAL COMPONENTS
Figure 3.1-1 shows the basic re'gisters and switching units of the 7100 CPU.
Because the registers and switching units have different requirements, they are
made up of various types of basic components which are explained below.
Shift Cell
A shift cell allows simultaneous read-in and read-out operations. Shift cells are
used to shift data to adjacent positions within a register, or to read out old data and
read in new data simultaneously.
The basic shift cell is shown in Figure 3. 1-2A. Two triggers have multiple inputs
to turn on the selected register position. The control lines "set" and "hold" are gen-
erated by the CP set pulse. Note that "hold" falls prior to the rise of "set" and rises
again prior to the fall of the set pulse. Refer to Figure 3.1-2B.
The numbers on the timing chart in Figure 3. 1-2B correspond to the test points of
Figure 3. 1-2A. With the input line active, the signal at test point 2 becomes active.
Test point 2 conditions the + TO with its output, test point 3, conditioning one leg of
the +TA. The set pulse conditions the other leg of the +TA. The output of this trigger,
test point 4, remains active for the duration of the set pulse. Test point 4 conditions
the lower +TO, so that test point 5 becomes active and conditions one leg of the +TA.
Because "hold" becomes active prior to the fall of the "set," the lower trigger latches
and retains the information.
The registers that contain shift cells are:
1. Storage register (SR)
2. Accumulator register (AC)
30 Multiplier-quotient register (MQ)
4. Index register (XR)
Triggers
A trigger acts as an information storage unit. Information can be read into a
trigger, and retained there until the trigger is reset.
The registers that contain triggers are:
1. Program register (PR)
2. Address register (AR)
3. Sense indicators (SI) (This register actually uses two triggers for each
position to permit complement operations; it should not be confused
with shift cell registers.)
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IBM 7090 Specifications

General

Category	Mainframe Computer
Introduced	1959
Transistor-based	Yes
Word Length	36 bits
Add Time	4.8 microseconds
Memory	Core memory
Memory (words)	32, 768 words