Foundations — High Bandwidth Memory (HBM - HBM2 - HBM3)

6.5.4 · D1 · Hardware › Advanced & Emerging Architectures › High Bandwidth Memory (HBM - HBM2 - HBM3)

Is page par koi assumption nahi hai. Parent note High Bandwidth Memory padhne se pehle, hum har woh word aur symbol build karte hain jis par woh note depend karta hai. Upar se neeche padho; har idea sirf upar waale ideas use karta hai.

1. "Bit" aur "byte" — woh units jisme sab kuch count hota hai

Yeh topic ko kyun chahiye: memory capacity aur bandwidth bytes mein measure hoti hai, lekin actual hardware bits ko wires se push karta hai. Jab bhi aage "8 se divide karo" dikhega, toh woh isliye hai kyunki hum wires ke bits ko bytes mein translate kar rahe hain.

2. "Wire / pin" aur "toggle" ka matlab

Figure dekho: har horizontal line ek wire hai. Jo wire quickly toggle karti hai woh zyada bits per second bhejti hai; jo wire slowly toggle karti hai woh kam bhejti hai. Ek single wire kabhi bhi ek hi waqt mein do bits nahi bhej sakti — isliye hi humein data fast move karne ke liye kaafi saari wires chahiye.

Yeh topic ko kyun chahiye: HBM ki headline "1024 wires" hai. Tum yeh nahi samajh sakte ki width kyun help karti hai jab tak yeh nahi dekha ki har extra wire ek independent lane hai jo apna bits ka stream carry karti hai.

3. Symbol $N$ — kitni data wires hain

4. Symbol $f$ — per-pin transfer rate, aur "Gbps" kyun

Figure mein ek clock wave (violet) dikhaya hai. Single data rate mein, ek bit ek full cycle mein aati hai. Double data rate (DDR) mein, bit dono up-edge aur down-edge par aati hai — same clock se double bits. Isliye "1 GHz DDR = 2 Gbps."

5. Dono ko milao — bandwidth formula

Memory Wall dekho yeh jaanne ke liye ki kyun hum yeh number badhane ke liye desperate hain, aur DDR vs GDDR vs HBM dekho ki do knobs alag memory families mein kaise alag-alag split hote hain.

6. Power per wire — symbols $P$, $C$, $V$

Yeh topic ko kyun chahiye: yeh HBM ki superpower explain karta hai. HBM apni wires chhoti rakhta hai (chhota $C$, kyunki woh processor ke paas ek tiny carrier par baithe hain), low-swing (chhota $V$), aur slow (chhota $f$). Chhota $C$, chhota $V^2$, chhota $f$ → tiny $P$ per wire. 1024 wires ke baad bhi total low rehta hai. Ise energy per bit (pJ/bit) ke roop mein measure karte hain.

7. Wires chhoti kyun ho sakti hain — physical stack

Figure ek side view hai. TSVs (magenta) DRAM dies ke through vertically jaate hain. Microbumps stack ko interposer (orange) par drop karte hain, jo GPU/processor ke paas baitha hai. Kyunki dono ek hi chhoti tray par hain, data wires printed circuit board ke centimetres ki jagah millimetres lambi hain — yahi geometric reason hai ki $C$ chhota kyun hai.

Yeh topic ko kyun chahiye: section 6 ka formula kehta hai chhoti wires power bachati hain, lekin koi bhi cheez physically wires ko chhota hone par majboor nahi karti. TSVs + interposer woh machinery hai jo unhe actually chhota banati hai. Compare karo GDDR Memory se, jahan chips board par door baithe hain.

8. "N-Hi" aur "channel" — height aur independence count karna

Prerequisite map

Aise padho: units bandwidth formula aur power formula ko feed karte hain; physical stack wires ko chhota banata hai (chhota $C$); saath mein yeh explain karte hain ki HBM wide + slow kyun choose karta hai.

Equipment checklist

Parent note ke liye tum ready ho jab yeh saab in mein se koi bhi zor se answer kar sako: