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3150 - Module #2
Stored Program Machine
| Question | Answer |
|---|---|
| What is a stored program machine? | A computer with a storage component that may contain both data to be manipulated and instructions to manipulate the data. Basically, the user is able to change the sequence of operations on the data. |
| What is the definition of a program? | A program is the sequence of operations performed on the data. It's a finite set of instructions that specify the operands, operations, and the sequence by which processing has to occur. |
| What is the definition of an instruction? | An instruction is a group of bits that tells the computer to perform a specific operation. It's composed of the operation and operand part. |
| What is the operation part of an instruction? | Also called the operation code (or op.code), it's a group of bits that defines the action to be performed. |
| For each machine the set of operations is _______ and _______. | limited, defined |
| In general, a machine with n bits as op.code is capable of ____________________________. | supporting 2^n distinct operations each having a distinct encoding as op.code. |
| What is the operand part of an instruction? | This defines the element(s) needed for operation. Besides the op.code, there's four things that make up the operand part: 2 source operands, 1 destination operand, and 1 operand to specify the location of the next instruction to be fetched. |
| What 5 classes are instructions grouped into? | 4, 3, 2, 1, and 0-address instructions. |
| Why do various addressing modes exist? | The ability to specify operands in different ways brings a greater degree of flexibility to the computer. |
| Specify the relationships between Stored Program Machines, Programs, and Instructions. | Instructions are a program and programs are a stored program machine. In other words, instructions make up a program and programs make up a stored program machine. |
| What is a 4-address instruction? | Each operand is worth 11 bits (4 operands, 44 bits), and all 4 operands are present. |
| What is a 3-address instruction? | You can imply the next instruction is right after the current one because most instructions are sequential. Therefore, you can use the program counter (PC) to increment addresses. |
| What is a 2-address instruction? | You can store the destination in one of the sources implicitly rather than explicitly defining the destination (uses the program counter as well here). |
| What is a 1-address instruction? | Rather than defining sources explicitly you can implicitly define a location in the system that the source always gets set to. You use the accumulator (A) which is always the replacement for the implied sources and destination operands. |
| What is a 0-address instruction? | You just use the stack where the operands are stored, so only the op.code exists now. Recalling last-in-first-out, you always have access to the top of the stack. For example, you pop two operands, do the operation, and push the result into the stack. |
| What is the point of various addressing modes? | This presents the ability to specify operands in different ways. This allows a greater degree of flexibility to the computer. |
| What is base addressing? | A variation of index mode which allows for relocatability. |
| How does a system know which addressing mode the instruction uses? (How does a system differentiate within itself what's just memory, a value, etc.?) | It has mode bit(s) within the operand bits. For example, 001 = direct, 000 = indirect, etc. This is how communication and managing is done within the system. |
| How does a computer know to execute a program? | The PC points to the first instruction. The first instruction is read, decoded from memory into machine language, and then executed. The system basically goes into sequence of cycles where the program fetches, decodes, and executes the instruction. |
| What are the steps to the flow of control and data within the computer? (What are the steps of the instruction cycle?) | 1) Program and data are read in and stored in main memory. 2) An instruction is fetched from main memory. 3) Fetched instruction is decoded. 4) Operand(s) are fetched. 5) Operation is performed. 6) Steps 2-5 are repeated till the end of the program. |
| What's a tag bit? | It's used to represent data (0) or address (1). |
| What happens during the fetch state of an instruction? | The current instruction is fetched from code memory and loaded into the instruction register. |
| What happens during the decode state of an instruction? | The instruction is decoded and any required operands are fetched from memory or from the register file. |
| What happens during the execute state of an instruction? | The instruction is executed. A result may be stored in a register or the accumulator. |
| What happens if an unexpected event happens during the execution of a program/instruction cycle? (Such as dividing by zero) Describe the process. | An interrupt mechanism that's built in takes hold. The interrupt allows the processor to finish what it's currently doing with its program and then simply leave that program and execute another program. |
| What is the program interrupt? | This is the transfer of control from the currently running program to another service program as a result of an external or internal generated request. Control might return to the original program after the service program is executed. |
| What are the three types of interrupt? | They are external, internal, and software interrupts. |
| What is an interrupt? | It's a signal to the processor that causes the processor, after completing its current instruction, to fetch the next instruction from a special location in memory. |
| What is the definition of a register? | It's a group of binary cells suitable for holding binary information. The bits in a register are numbered, either left-to-right or right-to-left, starting either from 0 or 1. |
| What is a parity error? | When sending bits, somehow a 0 or 1 gets flipped so it's incorrect. To fix this - parity bit. If there's originally an even number of 1's, parity bit is 1. If odd number of 1's exists in the end with the parity bit being 1, then there's been an error. |
| How do you make a computer execute faster? | There's two approaches: reduce the number of instruction cycles or reduce the duration of an instruction cycle. To do this, there's 2 options: you can increase clock rate or reduce the number of micro-operations. |
| What are the 4 types/traits of registers and their purposes? | These are the general purpose (no designed purpose), special purpose (register has a certain task, i.e. interrupt vector), storage type (storage only, no hardware attached), and operation type registers (extra hardware attached for operations). |
| What're the registers of the Wimp51? | The eight-bit accumulator (ACC), instruction register (IR), program counter (PC), auxiliary register (AUX), and R0-R7 registers. There's also the single-bit C and Z flags. |
| What're the logic units of the Wimp51? | AUX input multiplexer (MUX), control unit (CU), and two arithmetic and logic units (ALU and PCALU). |
| What does the PCALU of the Wimp51 do? | The PCALU manipulates the PC contents directly. This is especially important because the ALU is so far away from the PC. |
| What is the PSEN signal of the Wimp51? | The PSEN signal is an enable signal to I/O devices or memory and is a 1 bit signal. |
| What are two distinct advantages of dealing with different addressing modes? | Advantages are flexibility (some addressing modes work well with certain program designs while others do not) and speed (some addressing modes are faster than others so having this option to speed things up is huge). |
| Why is direct address mode faster than register address mode? | Although direct is fast, register mode is one of the fastest addressing modes. Accessing the main registers is extremely quick compared to other modes. |
| Is the following instruction valid? GOTO 30 | Yes. |
| Is the following instruction valid? ADD ACC, 25 | Yes. |
| Is the following instruction valid? Subtract 35, 25 | No, there's no storage destination. |
| What are two distinct disadvantages of dealing with different addressing modes? | Disadvantages are overhead (average time per instruction increases, making your system slower) and more space used (some addressing modes use more than others, so poorly written programs can cause more storage to be used). |
Created by:
bmcisme
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