Unit Model Paper · Computer Science SSC-II · Unit 1 · Computer Systems — Athens Academy Islamabad

Athens Academy Islamabad · Unit Model Paper

COMPUTER SCIENCE SSC–II

Unit 1 — Computer Systems

SECTION – A Multiple Choice Questions · on the portal

Section A of this unit is delivered on the Athens Content Studio portal, not on this sheet.

Unit 1 Quiz — timed multiple-choice practice
Unit 1 Flashcards — definitions, conversions and figures for recall

In the board paper, Section A is compulsory, carries no choice, and is collected separately before the rest of the paper is attempted.

SECTION – B (Marks 22) Short Questions

Q. 2 Answer the following questions briefly. Attempt all parts; each part offers a choice of two alternatives joined by OR. (11 x 2 = 22)

(i)	★ Convert $1101101_2$ into decimal, then express your answer in hexadecimal. OR State what positional value means, and use it to show why the digit 5 in $2F5_{16}$ is worth 5 while the digit 2 is worth 512.	1+1 1+1	Number systems Positional value
(ii)	★ Convert $45.625_{10}$ into binary. Show the working for the integer and fractional parts separately. OR ★ Define MSB and LSB, and identify each in the binary number $10110011_2$ .	1+1 1+1	Base conversion MSB / LSB
(iii)	★ Convert $5273_8$ into binary using grouping. State the group size you used and why. OR State how many bits represent one octal digit and how many represent one hexadecimal digit, and explain why these numbers are 3 and 4.	1.5+0.5 1.5+0.5	Grouping method Bits per digit
(iv)	Add the binary numbers $10110_2$ and $1101_2$ . Verify your answer by converting both numbers to decimal. OR Name any two of the four machine-level data types, and state how each is represented.	1+1 1+1	Binary arithmetic Data types
(v)	★ Subtract $011010_2$ from $100101_2$ using the 2's complement method. State clearly what you do with the carry. OR State what is done with the carry in the 1's complement method and in the 2's complement method, and name the term used for the 1's complement case.	1.5+0.5 1+1	Complements End-around carry
(vi)	★ Represent $-29$ in 8-bit 2's complement form. Show each step of your working. OR ★ Name the three components of a 32-bit IEEE 754 floating-point number and state how many bits each occupies.	2 1+1	Signed numbers IEEE 754
(vii)	An 8-bit unsigned register holds 200. The value 100 is added to it. State the result actually stored and name the condition that has occurred. OR Distinguish between system software and application software, giving one example of each.	1+1 1+1	Overflow Software types
(viii)	The character 'A' has ASCII code 65. Write its 8-bit binary code, and state the code for 'Z' in decimal. OR State the year Unicode was first released and the body that publishes it, and name any two UTF encodings.	1+1 1+1	ASCII Unicode
(ix)	★ A process is in the Blocked state and the resource it was waiting for becomes available. Name the state it moves to, and explain why it cannot move directly to Running. OR ★ Write any two differences between a process and a thread.	1+1 1+1	Process states Process vs thread
(x)	★ Two processes each hold a resource the other needs, and neither can continue. Name this condition and explain how it arises. OR ★ Distinguish between multiprogramming and multitasking with reference to when the CPU switches.	1+1 1+1	Deadlock OS types
(xi)	Name the three file allocation methods, and state one disadvantage of the contiguous method. OR Name any two types of software hosting, and state one advantage of each.	1.5+0.5 1+1	File allocation Software hosting

SECTION – C (Marks 20) Long Questions

Attempt the following questions. Marks of each question are equal. Each question offers a choice of two alternatives joined by OR. (4 x 5 = 20)

Q.3	★ Convert $179.257_{10}$ into binary. Show the division working for the integer part and the multiplication working for the fractional part, giving the fraction to seven binary places. State clearly in which direction each set of digits is read. OR Convert $6457_8$ into hexadecimal by both methods given in the unit — via decimal and via binary. Show every step, and state which method protects method marks in the examination and why.	2.5+2.5 2.5+2.5	Base conversion Octal ↔ Hex
Q.4	★ Represent $-72$ in 8-bit 2's complement form, showing each step. Then verify your answer by adding it to $+72$ and explain what the result proves. Finally, state the full range of an 8-bit signed number and of an 8-bit unsigned number. OR Explain the difference between signed and unsigned representation under the headings: sign bit, values represented, range for $n$ bits, and method used. Give the 8-bit range in each case.	2+1.5+1.5 1.25×4	Signed numbers Signed vs unsigned
Q.5	★ Three processes arrive together: P1 = 4 ms, P2 = 3 ms, P3 = 1 ms. Draw a dry-run table for the order P1, P2, P3 showing start time, finish time, waiting time and turnaround time for each. Repeat for the order P3, P2, P1. Calculate the average waiting time in each case and state which order is more efficient and why. OR Name and explain the six functions of an operating system. For each, write one line stating what it manages.	2+2+1 5	Process scheduling OS functions
Q.6	★ Compare ASCII and Unicode under the headings: bits used, number of characters, languages supported, and compatibility. Then state the binary code for the character 'A' and explain why a fixed-length coding scheme helps a computer store text efficiently. OR Name the five states of a process and explain what happens in each. State which state a process cannot enter directly from Blocked, and why.	1×4+1 1×5	ASCII vs Unicode Process states

SECTION – D Board Marking Pattern (Reference) not part of the examination

Section	Attempt	Marks	Where
A	Multiple choice, compulsory, no choice	See board paper	Athens portal — Quiz & Flashcards
B	All 11 parts, one alternative per part	11 × 2 = 22	On this sheet
C	All 4 questions, one alternative per question	4 × 5 = 20	On this sheet
Total	Sections B and C	42	On this sheet

Exam tip: The choice sits inside each question, not across the paper — you cannot skip a part, only choose which half to answer. Read both alternatives before writing a word, and pick on the strength of what you can actually produce: the side where you can show the division working, complete the table, or state every step. In this unit especially, a conversion you can finish is worth more than a definition you half-remember.

Final word from Athens Academy Islamabad. This unit is built on method, not memory. A base conversion, a 2's complement, a dry-run table — each has a fixed sequence of steps that earns marks as it goes, even when the final answer slips. Always show the working: the division column, the borrowed bit, the discarded carry. If a question here defeated you, return to that section of your notes, cover the page, and work the example again from the first line.

📃 Chapter 1 · Computer Systems — Chapter Model Paper

Chapter 1: Computer Systems Model Paper