One-Liners to Remember

Fundamentals

• The father of the computer is Charles Babbage; the first programmer is Ada Lovelace.
• First generation = vacuum tube; second = transistor; third = IC; fourth = microprocessor.
• 1 byte = 8 bits. 1 KB = 1,024 bytes.
• The brain of the computer is the CPU. The CU controls; the ALU calculates.
• RAM is volatile, ROM is non-volatile. Cache is the fastest memory after registers.
• MICR = cheques, OMR = answer sheets, OCR = text recognition, barcode = shop bills.
• Binary 2, octal 8, decimal 10, hex 16. ASCII is 7-bit (128 characters); Unicode covers all languages.
• NAND and NOR are universal gates.

Software and OS

• Compiler = whole program, interpreter = line by line.
• Linux was created by Linus Torvalds (1991). It is open source.
• Shift + Delete = permanent delete. Ctrl + Shift + Esc = Task Manager. Win + L = lock.
• Paging = fixed blocks; segmentation = variable blocks.
• Deadlock needs four conditions: mutual exclusion, hold and wait, no pre-emption, circular wait.

Networking and security

• The Internet is a WAN; Bluetooth is a PAN.
• The router works at the Network layer (IP); the switch at the Data Link layer (MAC); the hub at the Physical layer.
• IPv4 = 32 bits; IPv6 = 128 bits; MAC = 48 bits.
• HTTP 80, HTTPS 443, FTP 21, SSH 22, SMTP 25, DNS 53, POP3 110, IMAP 143.
• Virus needs a host; worm spreads alone; trojan hides in a useful program.
• Symmetric encryption uses one key; asymmetric uses a key pair. A digital signature uses the sender's private key.
• IT Act 2000; section 66C = identity theft; 66D = cheating by personation; 66F = cyber terrorism.
• Cyber fraud helpline: 1930.

Office and Excel

• Excel: 1,048,576 rows, 16,384 columns (XFD), sheet name up to 31 characters.
• Formula starts with =. F4 toggles absolute reference. F2 edits a cell. Alt + = is AutoSum.
• SUMIF = (range, criteria, sum_range). SUMIFS = (sum_range, range1, criteria1, ...).
• VLOOKUP cannot look left. Use FALSE for an exact match.
• FIND is case-sensitive; SEARCH is not. SUBSTITUTE replaces text; REPLACE replaces by position.
• INT(-4.5) = -5; TRUNC(-4.5) = -4. MOD takes the sign of the divisor.
• PMT = EMI, FV = future value, PV = present value, NPV and IRR = investment appraisal.
• Pivot table does not refresh by itself. Alt + F5 refreshes.
• Word: mail merge = main document + data source. Ctrl + Enter = page break.
• PowerPoint: F5 = start from beginning; Shift + F5 = from current slide.

Database and technology

• Primary key = unique + not null. Foreign key links two tables. Degree = columns; cardinality = rows.
• WHERE filters rows; HAVING filters groups.
• DELETE removes rows; TRUNCATE removes all rows; DROP removes the table.
• Stack = LIFO; queue = FIFO. Binary search needs a sorted list.
• IaaS, PaaS, SaaS are the three cloud service models.
• Digital India launched 1 July 2015. UPI launched 2016. 5G launched in India on 1 October 2022.