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21264/EV68A Hardware Reference Manual
Internal Architecture 2–3
21264/EV68A Microarchitecture
Figure 2–1 21264/EV68A Block Diagram
2.1.1.2 Branch Predictor
The branch predictor is composed of three units: the local, global, and choice predic-
tors. Figure 2–2 shows how the branch predictor generates the predicted branch
address.
INT
UNIT
1
(U1)
Address
ALU 1
(L1)
Address
ALU 0
(L0)
Branch
Predictor
VPC
Queue
INT
UNIT
0
(U0)
Integer Registers 1
(80 Registers)
Integer Registers 0
(80 Registers)
Ebox
FP
ADD
DIV
SQRT
FP
MUL
FP Registers
(72 Registers)
Fbox
Dual-Ported Data Cache
Physical
Address
Mbox
DTB
(Dual-ported, 128-entry)
Load
Queue
Store
Queue
Miss Address
File
Arbiter
Victim
Buffer
IOWB
Duplicate
Tag Store
Probe
Queue
Cache
Data
128
Cache
Index
20
System
Bus
64
System
Address
15
128
Cbox
FP Issue Queue
(15 Entries)
Integer Issue Queue
(20 Entries)
Ibox
Decode and
Rename Registers
Retire
Unit
ITB
Predecode
Fetch Unit
Next Address
Virtual Address
Four
Instructions
Instruction Cache
128
Physical
Address
Data
Data
FM-
056
42-AI4